HK alloy is a member of the heat resistant cast alloy family (H-Series) steels. They are widely used in the petrochemical industry for components requiring enhanced high temperature properties. Microstructural changes occurring at high temperature clearly affects its mechanical properties. These properties have been shown in HK-40 steel subjected to high-temperature degradation and prone to the formation of sigma phase. The investigation carried out included metallurgical analysis, materials characterization and mechanical analysis. Metallurgical analysis included advanced metallography techniques to characterize its microstructure morphology and properties. Significant depletion of vital precipitates observed that definitely degraded its high temperature properties. Mechanical analysis included hardness profile, tensile testing of samples taken from the tree supports and tested in room temperature and in 800°C environments. Experimental results revealed that the structure of HK-40 affected by the formation of the high temperature brittle sigma-σ-phase. Nonetheless, mechanical properties did not suffer much at higher temperature.

A furnace tube support failed after 6 months service at 850°C. The support was an HK alloy, a member of the heat-resistant cast alloy family (H-Series) steels. The H-series steels are widely used in the petrochemical industry for components requiring enhanced hightemperature properties. Microstructural changes occurring at high temperature clearly affect the mechanical properties. The property degradation in HK-40 steel furnace tube support subjected to high temperature was caused by the formation of sigma phase. The investigation included metallurgical analysis, materials characterization, and mechanical analysis.